Cameron Mitchell

Assistant Professor

Research Classification

Research Interests

Aging
molecular biology
Muscle hypertrophy
Nutrition
Physical performance
Protein metabolism
Resistance training
Sarcopenia

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Graduate Student Supervision

Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Short-term resistance exercise training attenuates muscle damage and alters transcription of muscle extracellular matrix regulators in response to 300 eccentric contractions in young adults (2023)

A maximal eccentric (ECC) bout can confer protection by reducing exercise-induced muscle damage (EIMD) following a subsequent ECC bout, this is known as the repeated bout effect (RBE), a phenomenon that results in large non-specific translational and transcriptional responses. Resistance exercise training (RET) stimulates similar adaptations which becomes more refined with continuing training. It was hypothesized that RET and RBE may share a common mechanism involving remodeling of the extracellular matrix (ECM). Healthy young adults (6 female, 10 males; 20.9 4.1 years) performed 6 sessions of unilateral RET with the contralateral leg acting as a control prior to 2 bilateral bouts (B1, B2) of 300 eccentric knee extensions separated by 21 d. Bilateral muscle biopsies were obtained before and 48-hours after each bout. Muscle damage assessed as the area under the curve for isometric force loss over 72-hours following ECC, was attenuated in B1 by RET (42%±4.76, p=0.035). Protection conferred by B1, resulted in complete recovery of force loss by 48h. ECC elevated expression of Transforming Growth Factor-Beta (TGF?, p=0.018) and Collagen Type IV (COL4A1, p=0.027) only in the RET leg after each bout, while Matrix Metalloproteinase-2 (MMP2) mRNA increased after ECC only in the control leg (p=0.049). These results collectively suggest that short-term RET modifies the transcriptional response of ECM regulators to bouts of high volume ECC exercise which may partially underpin the observed attenuation of ECC induced EIMD by prior RET. Further analysis is required to determine if altered transcription of ECM regulators is also reflected at the protein level.

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The effects of essential and non-essential amino acids on post-exercise anabolic signaling and transcriptional regulators of the intramuscular extracellular matrix in young males : a randomized controlled trial (2023)

Skeletal muscle is composed of myofibers surrounded by an extracellular matrix (ECM) primarily containing collagen. Essential amino acid (EAA) consumption is known to increase post-exercise myofiber anabolism, but it is unknown if post-exercise ECM remodeling is nutrient-sensitive. Seventeen males (21.1±3.3 years) completed combined plyometric and resistance exercise and received biopsies of the vastus lateralis collected before, 2 and 4 hours post-exercise to assess the mechanistic target of rapamycin (mTOR) pathway activation and transcriptional regulators of ECM turnover. Blood was also drawn from an antecubital vein to measure plasma amino acid concentrations prior to and following supplement consumption and resistance exercise. Immediately after exercise, participants consumed 15g of either a carbohydrate placebo, EAA, or a vitamin C enriched collagen peptide (enriched in non-essential amino acids) supplement; each participant completed two of the three randomized conditions. EAA supplementation increased plasma amino acid concentrations of EAAs and leucine (p ≤ 0.001), whereas collagen peptide supplementation increased concentrations of non-essential amino acids (NEAA), glycine, proline, and hydroxyproline (p ≤ 0.018), there was no effect of carbohydrate consumption on plasma amino acid concentrations. rpS6Ser235/236 and rpS6Ser240/244 phosphorylation following EAA supplementation resulted in a larger and more prolonged anabolic signaling response, at 2 and 4 hours post-exercise, respectively, compared to the collagen peptide and placebo conditions (p ≤ 0.036). Anabolic signaling increased in the collagen peptide and placebo conditions similarly post-exercise. There was no effect of exercise or nutrition on mRNA expression of ECM regulators; however, a main effect of time for connected tissue growth factor (CTGF) demonstrated an increased expression from 0 to 2 hours (p = 0.014). These findings suggest that mTOR pathway activation is upregulated post-exercise and further increased with EAA supplementation, while the acute transcriptional ECM regulators are independent of exercise and plasma amino acid availability in the hours following exercise. Further analysis will directly measure the effects of post-exercise nutrition on myofibrillar and skeletal muscle ECM protein synthesis.

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The effects of higher- and lower-load resistance exercise training on leg and arm skeletal muscle mass in healthy young adult females: a randomized equivalence trial (2022)

Resistance exercise training (RET) is potent stimulus to induce muscle growth. Heavier loads are traditionally more effective compared to lighter loads for inducing muscle growth, but recent research has demonstrated that lighter load (LL) RET can lead to similar muscle hypertrophy as higher load (HL) RET when training to volitional fatigue. While these results have been consistently shown in males, there is limited research on this topic using female participants. The aim of this study was to compare the muscle hypertrophic response to HL and LL RET in the upper and lower body of young adult females. It was hypothesized that there would be an equivalent increase between the HL and LL RET in both the upper and lower body. A randomized repeated measures within-participant design was utilized where each participant had one arm and leg assigned to train with HL and the other limbs assigned to train with LL. Participants trained thrice weekly for 10-weeks, performing unilateral knee extension and unilateral dumbbell bicep preacher curls. Biceps brachii thickness increased following both LL and HL RET (∆LL = 0.3±0.4 cm, ∆HL = 0.2±0.4 cm, Interaction P = 0.12), but upper arm lean mass only increased following LL RET (∆LL = 0.1±0.2 kg, ∆HL = 0.04±0.2 kg, Interaction P = 0.02). Neither HL nor LL RET induced an increase in any measure of lower body muscle size. LL RET induced a greater training volume compared to HL RET in the arms due to similar absolute loads used during training. In the lower body, training volume must be considered as neither loading condition reached the necessary total training volume required to induce measurable muscle growth.

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The impact of abdominal body contouring surgery on physical function after a massive weight loss: a pilot non-randomized controlled trial (2021)

Background: It is estimated that 70% of individuals who undergo a massive weight loss (MWL) develop excess skin (ES). The ES around the abdominal area has been shown through patient reported outcome measures to negatively impact perceptions of physical function. Yet no studies have examined the impact of abdominal body contouring surgeries on direct measures of physical function.Study Objectives: The primary objective of this pilot study was to determine the variability of outcome measures in the context of ceiling, floor and learning effects to allow measuring the test-retest reliability of the physical performance measures. The secondary objectives of this study were to measure recruitment/retention, participant’s acceptability, and adherence to the protocol. The tertiary objective of this study was to provide data to estimate the effect size and sample size required to design a definitive non-randomized controlled trial.Materials and Methods: Patients who have undergone MWL were recruited through 4 medical clinics and were placed in either body contouring intervention group if they self-selected to undergo surgery or post massive weight loss matched control group. They participated in a series of physical function batteries of tests including 9-item modified physical performance test, 30s-chair to stand, star excursion balance test, timed up and go, modified agility t-test, 6-minute walk test, and body composition measures of fat mass and bone free fat free mass. There was a total of two visits which were 8-12 weeks apart to accommodate for recovery time for abdominal contouring procedures.Conclusion: It was found that tests involving dynamic balance, agility, and walking were reliable and showed medium to large effect size to be considered for future studies. Retention (72%) and recruitment (46%) rates were found to be compromised due to Covid-19 pandemic local limitations, and institutional surgical regulations. Depending on the primary outcomes of future trials, it is estimated that between 12 to 37 participants are required to be included in the sample size to achieve adequate statistical power.

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